I happened to find the article below while searching for the elusive source of a possible vacuum leak in my 81 380sl. According to the article, vacuum leaks can be caused by a valve cover gasket, oil cap gasket, and even the rubber grommet on the dipstick.

Pelican Technical Article: Mercedes Benz - Fixing Common Vacuum Leaks


Can these things really affect an engine as significantly as the article suggest?

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1981 380SL
Chassis: R107.045

That does sound strange doesn't it? The valve cover gasket, oil cap gasket and rubber grommet on the dipstick would all be stopping crank case pressure from escaping wouldn't they? The article mentions how the crank case pressure is regulated by the PCV valve but it doesn't specify the relationship between crank case pressure and vacuum pressure which is created in the throttle body. I would have thought that these systems are kept separate - but as I'm a newbie to these petrol Mercedes engines I await the advice of others...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

my understanding is they create a vacumm in the crankcase to draw fresh air thru it,and suck the air out at the same time.Strangest system I've seen.as on my car i believe a blow by valve is damaged,so if I can't clean it,I will block vac line to crankcase valve cover and vent thru the top,to throttle body.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

I can't access the M104 FSM so I can't speak for that and the M103 chapters on startek (W201) seem to be missing the description of crank case breathing...

...the M102, however, seems to have a conventional crank case breathing system.

I don't see how they can create a vacuum without some sort of mechanical device if they don't use a venturi - so OK I guess I'm a bit restricted in knowledge on this subject but I've only come across vacuum being made in an automotive context by either a vacuum pump or air flow through a venturi.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I think valve covers causing vacuum leaks is only true of cars that use an oil separator that has vacuum pulled on it. On the M117 in my 350SL as well as my M102 in my 190E 2.0 the crankcase vent goes straight to the air cleaner and is effectively venting at atmospheric pressure, not under vacuum.

That article more than likely doesn't apply to your M116.


To answer you question otherwise, yes they can be somewhat significant I've seen people over tighten BMW valve covers which are plastic, crack them, and see a vacuum leak.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Your explanation makes a lot of sense -- except for the fact that the person who wrote the article applied it to the M104 which, AFAIK, does not have the vacuum system you mentioned. Moreover, he wrote that the "concepts I'll go over apply to nearly all fuel-injected gasoline engines."

So, either he was mistaken, or he knows something about vacuum leaks nobody else seems to know???

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1981 380SL
Chassis: R107.045